This invention relates to round tenon joints in the furniture industry, particularly tenon joints for chair legs, spindles, and other wood parts wherein a round tenon is inserted into a mortise or blind hole and secured therein with glue.
Round tenon joints are traditional in the furniture industry and are the most common joints used in the manufacture of wooden chairs. Chair legs have a tenon on one end, while spindles and other wooden parts which form joints at both ends on assembly have tenons on each end.
Round tenon joints have a number of major disadvantages. First, the tolerance between the tenon and the hole into which it fits must be very closely controlled for a press fit. If the joint is too loose, it will come apart. If there is insufficient clearance between the dimensions of the mortise hole and the tenon, the parts will not fit together easily, and assembly will be difficult. Further, glue that is placed in the joint during assembly is mostly wiped to the bottom of the mortise hole, leaving little or no glue on the tenon to interface with the inner surface of the hole, which creates a very weak joint.
It is known from U.S. Pat. No. 2,702,926 that a compressed dowel pin having longitudinal grooves can be employed in a conventional mortise to effect even distribution of glue between the pin and the mortise and form a strong bond under substantial pressure. The present invention is a machine for forming such grooves onto a round, shouldered tenon, such as on the end of a chair leg. A grooving machine for accomplishing the same objective is shown in MacQueston Pat. No. 3,651,483, in which a workpiece having a tenon at one end or at each end is held in a stationary position, and a movable die, characterized as an annular compressor fluting die, moves onto the work piece, cutting flutes into the tenon. A different fluting tool is used for each diameter of tenon which is to be processed. Centering of the workpiece is also necessary to achieve a properly centered fluted tenon.
Rahaim, in U.S. Pat. No. 2,702,926, teaches that a dowel can be compressed by a series of opposed grooved rolls. He finds it important that the grooving and contracting of the dowel does not create such a violent compression as to crush the dowel fibers.
The present invention both grooves and compresses a round tenon for a mortise and tenon joint, particularly for the manufacture of furniture. The present invention has several distinct advantages over the teachings of the prior art, the principal advantages being:
(1) Grooving of the tenon allows glue to remain within the joint rather than being wiped to the bottom of the mortise hole upon assembly, and weakening the joint. PA1 (2) Compressing of the tenon creates an expanding force within the joint at the time the compressed fibers react to the moisture of the glue. PA1 (3) The invented apparatus has the ability to compress the tenon to a well controlled, accurate diameter. PA1 (4) The invented apparatus is also adaptable to other manufacturing systems, for example, it can stand alone as a single end crimping machine, or it can be readily modified to a double end crimping machine. None of the other systems taught in the art can do this.
Currently-used machines employ a hand-feeding method wherein an operator must place the tenon in the operative position in the crimping mechanism. The present invention is a totally automatic mechanism in which one workpiece, or a series of wooden workpieces, each having a tenon end or ends, are fed into position for crimping, crimping of the tenon, or tenons, is accomplished, and the workpiece is ejected.